This invention relates generally to the field of devices that provide a fluid-tight seal between a flexible sheet or membrane and a rigid member extending through the sheet or membrane. More specifically, the present invention relates to a coupling or "boot" that provides a fluid-tight seal around a gas conduit or pipe that extends through a flexible sheet covering a landfill or the like.
Landfills continue to be one of the principal means used for the disposal of solid waste, and particularly biodegradable waste materials. In recent years, increased attention has been paid to environmental concerns in the design, construction, and use of solid waste landfills, leading to innovations that substantially mitigate the environmental impact of such landfills.
Among the recent innovations are those that provide for the compaction of the solid waste, thereby increasing the capacity of the landfill. An example of a modern landfill compaction system is disclosed in U.S. Pat. No. 4,838,733--Katz. In such landfill compaction systems, the landfill is covered with a flexible, fluid-impermeable barrier sheet. The barrier sheet is penetrated by gas vent pipes for venting methane gas generated by the decomposition of organic matter within the landfill. The vent pipes typically conduct the gas to a storage tank or a facility where the vented gas can be burned off.
Environmental considerations require the vented gas to be isolated from the atmosphere. Therefore, a gas-tight seal must be provided between each of the vent pipes and the barrier sheet. Because the sheet moves vertically with respect to the pipes, due to settling and compaction of the landfill, the seals between the pipes and the sheet must likewise move vertically (or axially), while maintaining seal integrity. Thus, for example, the system described in the above-mentioned Katz patent employs a lower collar slidably fitting around each pipe, and joined to the sheet with a gas-tight seal. The lower collar is joined to a fixed upper collar by a bellows-like sealing sleeve. Subsidence of the landfill is accommodated by the downward movement of the lower collar and the vertical extension of the sealing sleeve, thus maintaining seal integrity.
One disadvantage of the above-described seal structure is that the range of vertical movement is limited by the placement of the fixed upper collar. Thus, subsidence below a certain level will require replacement of the seal structure, while a sudden sinking of the landfill (due to, for example, a shifting of the landfill material or the underlying ground) could result in breakage of the seal.
Another prior art approach is the use of what is termed a "penetration sleeve". The penetration sleeve is a hollow tubular sleeve that fits around the pipe and extends from below the barrier sheet, through a hole in the barrier sheet, to above the sand and soil layers that are typically placed on top of the barrier sheet. The barrier sheet material surrounding the hole is formed into a tubular boot that is sealed around the exterior of the penetration sleeve. The diameter of the penetration sleeve is greater than that of the pipe, and the space between the sleeve and the pipe is filled with a substance such as bentonite. This approach has two major shortcomings: (1) The bentonite filler tends to dessicate and shrink, thereby degrading the seal between the boot portion of the barrier sheet and the pipe; and (2) there is little or no tolerance for relative movement between the penetration sleeve and the boot portion of the barrier sheet.
Thus, there has been a need for a sealing structure that can accommodate extreme and sudden vertical movements of the landfill, while maintaining seal integrity. Furthermore, there has been a need for such a sealing structure that is inexpensive, easily installed, durable, and weather-resistant.